1. Field of the Invention
The present invention relates to a sensor, and, more particularly, to a sensor assembly.
2. Description of the Related Art
Electronic devices are an increasing part of everyday life and they are presently integrated in a large number of products, including products traditionally thought of as mechanical in nature, such as automobiles. To bridge the gap between mechanical movement and electronic control it is necessary to successfully integrate electronic and mechanical components. The gap is normally bridged by using devices such as sensors and actuators.
Position sensors are used to electronically monitor the position or movement of a mechanical component. The position sensor produces data that may be expressed as an electrical signal that varies as the position of the mechanical component changes. Position sensors are an important part of innumerable products, providing the opportunity for intelligent control of a mechanical device.
Various contact type sensors are known. For example, potentiometers are used which detect a change in an electrical signal due to the physical change in position of a wiping contact on a resistive element. Rotational position movement can be detected by coupling a shaft of a potentiometer to the shaft of a rotating mechanical component. Linear movement can be detected using either a liner potentiometer or a rotating potentiometer that is coupled to a linear moving component using pulleys and a string or a belt to translate a linear motion to rotational motion. A problem with this type of sensor is the physical wearing of the rotating part, the wiping contact and the resistive element cause a drift in the electrical signal and lead to ultimate failure of the device.
Magnetic position sensors are generally a non-contact type of sensor and consist of a magnetic field sensing device which is usually stationary and a magnet attached to a moving component. As the magnet approaches the sensing device the magnetic field of the magnet is detected and the sensing device generates an electrical signal that is then used for counting, display, recording and/or control purposes. A problem with such sensors is that they depend on movement of the magnet and they are not able to provide information as to the static position of a mechanical component.
Other magnetic position sensors provide an indication of the displacement of the mechanical component by using a magnetic field sensing device which reports the intensity of a magnetic field from a magnet which is positioned on the mechanical component. The magnet is positioned and the magnetic field sensing device is located relative to the magnet in such a fashion as to cause the magnetic field to vary in the magnetic field sensing device as the magnet moves. A magnetic field sensing device may detect a static magnetic field from the magnet and report the field strength as a representation of the position of the mechanical component.
A magnetic positional sensor developed by the inventor, patented as U.S. Pat. No. 5,818,223, entitled xe2x80x9cROTARY POSITION SENSOR WITH CIRCULAR MAGNETxe2x80x9d, discloses a Hall effect device disposed within a cylindrically shaped magnet. The magnet having a magnetic field that varies from a north pole to a south pole as detected along a circular face of the magnet. The cylindrical magnet is mounted to a rotatable mechanical component and a Hall effect device is positioned inside the cylindrical magnet with an air gap therearound. The Hall effect device has flux concentrators mounted thereto. The magnetic field produced by the cylindrical magnet is detected by the Hall effect device which in response thereto produces an electrical response representative of the magnet and hence the mechanical component""s angular position.
A problem with such sensors is that they require large magnets and many are particularly sensitive to air gap variations.
Another problem with rotating sensors is that they require a stationary and a movable portion within a single assembly.
What is needed in the art is a compact modular position sensor which will provide static and moving position information using smaller magnets.
The present invention provides a position sensor assembly with a magnetic flux responsive device, a magnetic source and a ferrous target which alters the magnetic field permeating the magnetic flux responsive device and thereby producing an electrical signal. The electrical signal is representative of the position of the ferrous target.
The invention comprises, in one form thereof, a sensor assembly for detection of changes in magnetic fields including a magnetic flux responsive device and at least one magnet fixedly adjacent to the magnetic flux responsive device.
In another form, the invention provides a sensor assembly for sensing position, velocity, acceleration or change of acceleration. The assembly includes at least one magnet, each magnet having a north and south pole and a magnetic axis defined therebetween; a magnetic flux responsive device, each magnet being fixedly adjacent to the magnetic flux responsive device; and a ferrous target selectively movable relative to the at least one magnet.
In yet another form, the invention provides a method for sensing position, velocity, acceleration or change of acceleration including the steps of positioning a magnetic flux responsive device fixedly adjacent to at least one magnet, the magnetic flux responsive device including at least one electrical output; moving a ferrous target relative to the magnetic flux responsive device, the ferrous target configured to alter the magnetic field in the magnetic flux responsive device when the ferrous target and the magnetic flux responsive device are moved relative to each other; and calculating position, velocity, acceleration and/or change of acceleration from an electrical signal provided via the electrical output of the magnetic flux responsive device.
In yet still another form, the invention provides a method for controlling position, velocity, acceleration and/or change of acceleration including the steps of positioning a magnetic flux responsive device fixedly adjacent to at least one magnet, the magnetic flux responsive device including at least one output, locating a ferrous target relative to the magnetic flux responsive device, the magnetic flux responsive device outputting sensor data on the at least one output based on a position of the ferrous target; mounting the ferrous target to a movable structure and the magnetic responsive device to an other structure, calculating position, velocity, acceleration and/or change of acceleration of the ferrous target using the sensor data and thereby providing calculated information; receiving operator input; producing a control signal using the calculated information and the operator input; and actuating a positioning apparatus based on the control signal, the positioning apparatus being connected to the movable structure.
An advantage of the present invention is that a modular cost effective sensor is provided.
Another advantage is that a mechanical device may have a ferrous target attached thereto and the sensor of the present invention may be separately positioned relative to the ferrous target.